Toyota 2GR-FE Manual page 325

DTC P0121
DESCRIPTION
HINT:
This ETC (Electrical Throttle Control System) does not use a throttle cable.
The Throttle Position (TP) sensor is mounted on the throttle body, and detects the opening angle of the
throttle valve. This sensor is a non-contact type, and uses Hall-effect elements, in order to yield accurate
signals, even in extreme driving conditions, such as at high speeds as well as very low speeds.
The TP sensor has two sensor circuits which each transmits a signal, VTA1 and VTA2. VTA1 is used to
detect the throttle valve angle and VTA2 is used to detect malfunctions in VTA1. The sensor signal
voltages vary between 0 V and 5 V in proportion to the throttle valve opening angle, and are transmitted to
the VTA terminals of the ECM.
As the valve closes, the sensor output voltage decreases and as the valve opens, the sensor output
voltage increases. The ECM calculates the throttle valve opening angle according to these signals and
controls the throttle actuator in response to driver inputs. These signals are also used in calculations such
as air-fuel ratio correction, power increase correction and fuel-cut control.
2GR-FE ENGINE CONTROL SYSTEM – SFI SYSTEM
Throttle / Pedal Position Sensor / Switch "A"
Circuit Range / Performance Problem
ES–169
ES